CompSci516 Database Systems .edu

CompSci 516

Database Systems

Lecture 4

SQL

Instructor: Sudeepa Roy

Duke CS, Fall 2019

CompSci 516: Database Systems

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Announcements

? Lab-1 makeup instructions sent on piazza

? Please respond by 3 pm today if you have missed the lab

? Let me know if you are still not on piazza ? HW1 will be posted after the class

? On sakai (data is already there) ? Deadlines in stages ? First deadline on 09/17

Duke CS, Fall 2019

CompSci 516: Database Systems

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Today's topic

? Finish SQL ? RC

? Next week:

? Tuesday: Guest Lecture by Junyang Gao: RA ? Thursday: Lab on RA

Duke CS, Fall 2019

Acknowledgement:

The following slides have been created adapting the

instructor material of the [RG] book provided by the authors

ComDpr.SRcia5m16a:kDraisthabnaasne SaynsdtemDsr. Gehrke.

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Nulls and Views in SQL

Duke CS, Fall 2019

CompSci 516: Database Systems

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Null Values

? Field values in a tuple are sometimes

? unknown, e.g., a rating has not been assigned, or ? inapplicable, e.g., no spouse's name ? SQL provides a special value null for such situations.

Duke CS, Fall 2019

CompSci 516: Database Systems

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